Liquid-crystal display device, compensator layer and method of manufacturing retardation foil

ABSTRACT

A method of forming a liquid-crystal display device having a display cell comprises forming retardation foils on substrates using polymerized or vitrified liquid-crystal material wherein the liquid-crystal molecules of the polymerized or vitrified liquid-crystal material have a tilt angle with respect to a plane parallel to the substrates and so that the retardation foils have substantially complementary indicatrices and so that each one of the retardation foils brings about the compensation of approximately half the display cell in the driven state.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a divisional of U.S. patentapplication Ser. No. 08/857,756 filed on May 15, 1997 in the name ofPeter Van De Witte et al., the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a liquid-crystal display device having adisplay cell which comprises a layer of a nematic, liquid-crystalmaterial between two substantially parallel substrates, which displaycell is further provided with polarizers. The invention further relatesto a compensator layer which can be used, for example, in liquid-crystaldisplay devices, and to a method of manufacturing a retardation foil.

[0004] 2. Description of the Related Art

[0005] Liquid-crystal display devices are generally used, for example,in monitors, TV applications and, for example, display devices inmotorcars and for measuring instruments. The retardation foils can alsobe used in electro-optical modulators, for example, in welding gogglesand in passive optical elements, such as microscopes and optical systemsfor optical data processing.

[0006] A display device of the type mentioned in the opening paragraphis known from U.S. Pat. No. 5,210,630. In said display device, acompensator foil consisting of an optically anisotropic layer of acholesterically ordered polymeric material is used to counteractdiscoloration in a twisted nematic display device and to attain a highcontrast. The polymeric material is ordered in such a manner that amolecular helix can be distinguished, the axis of the helix beingdirected at right angles to the layer.

[0007] However, display devices comprising such a compensator still havea great angle-dependence; this is to be understood to mean that thecontrast is governed to a substantial degree by the angle or directionfrom which the display device is viewed.

[0008] One of the objects of the invention is to provide a displaydevice of the type mentioned in the opening paragraph, in which theangle-dependence is reduced considerably. A further object of theinvention is to provide a compensator layer which can be used, interalia, in such display devices.

[0009] Therefore, a display device in accordance with the invention ischaracterized in that the display cell comprises at least tworetardation foils which predominantly contain polymerized or vitrifiedliquid-crystalline material, the liquid-crystal molecules in thepolymerized liquid-crystalline material exhibiting a tilt angle relativeto the substrates, and the average directions of orientation of theliquid-crystal molecules in the polymerized or vitrifiedliquid-crystalline material of each of the retardation foils making anangle with each other which ranges between 60 and 120 degrees, viewed atright angles to the substrates.

[0010] The polymerized, liquid-crystalline material may be partlypolymerized, but, preferably, it is polymerized substantiallycompletely.

[0011] In this context, the direction of orientation of a liquid-crystalmolecule is to be understood to mean the perpendicular projection on asubstrate of the director of the liquid-crystal molecule. A retardationfoil is to be understood to mean a birefringent foil or layer or a foilor layer having an optically compensating or delaying effect (anoptically anisotropic layer).

[0012] The invention is inter alia based on the recognition that as aresult of the tilt angle of the liquid-crystal molecules in thepolymerized or vitrified liquid-crystal material, the retardation of oneof the retardation foils compensates, as it were, for the retardation ofa part of the liquid-crystal molecules in the display cell in the drivenstate; the retardation of the other retardation foil compensates, as itwere, for the retardation of another part of the liquid-crystalmolecules in the display cell in the driven state.

[0013] The invention is further based on the recognition that suchlayers of a polymerized liquid-crystal material can be manufactured in asimple manner, for example, by “spin-coating” of nematic liquid-crystalmaterials or by polymerization in the smectic C phase or byvitrification. Dependent upon the manner in which they have beenmanufactured, the liquid-crystal molecules in the polymerizedliquid-crystalline material exhibit a tilt angle relative to thesubstrates, which varies (for example by using surface-active materials)or which is practically constant. This can be determined by means ofconoscopy or microscopy using polarized light (polarizing microscopy).

[0014] A preferred embodiment of a display device in accordance with theinvention is characterized in that the direction of orientation of theliquid-crystal molecules in the polymerized or vitrifiedliquid-crystalline material is substantially constant in at least one ofthe retardation foils.

[0015] In a liquid-crystal display device in which the customary voltageis applied across the liquid-crystal material in the on-state, thedirectors in this material actually still make a small angle with thedirection perpendicular to the substrates. As a result, thebirefringence is different at different viewing angles andnon-symmetrical with respect to a direction perpendicular to the twosubstrates, which explains the angle-dependence of a liquid crystalhaving a nematic structure. This birefringence is caused, as it were, bytwo partial layers of a liquid-crystal material in which the opticalproperties of a partial layer are governed by the average tilt angle inthe relevant partial layer with respect to the substrates and by theaverage direction of orientation; if a sufficiently high voltage isapplied across the liquid-crystal layer, then the average direction oforientation in the partial layer is approximately equal to the directionof orientation, as determined by the orientation layers on thesubstrate, so that the magnitude of the difference between thedirections of orientation of the two partial layers is practically equalto the tilt angle. In accordance with the invention, theangle-dependence can be substantially eliminated by causing the averagedirections of orientation of the liquid-crystal molecules in thepolymerized liquid-crystalline material of the retardation foils tointersect each other at an angle which is practically constant (forexample equal to the twist angle of the display cell). The tilt anglesof the liquid-crystal molecules in the polymerized liquid-crystallinematerial can be set relative to the substrates, such that thecompensator composed of the retardation foils compensates theangle-dependence of the cell substantially completely.

[0016] During the manufacture of a retardation foil, the tilt of theliquid-crystal molecules (director profile) can be obtained by using apolymeric (or vitrified) material which is formed from a liquid-crystalmonomer.

[0017] In principle, any liquid-crystalline polymeric materials can beused to produce the material for the retardation foils. However, use ispreferably made of liquid-crystalline polymeric materials which are thereaction product of monomers or of a mixture of monomers comprising areactive group. Such polymeric materials have the advantage that theliquid-crystalline groups can be oriented prior to polymerization.Polymerization causes such an orientation to be frozen as it were. It isnoted that such a mixture may also comprise non-reactiveliquid-crystalline monomers. The reactive monomers preferably comprise aliquid-crystalline group.

[0018] For the reactive group use can be made of vinyl ethers, thiolenesystems or epoxy groups. However, use is preferably made of reactivegroups in the form of (meth)acrylate groups. Monomers comprising a(n)(meth)acrylate group proved to be excellently processable. In principle,the monomers can be thermally polymerized. In practice,radical-polymerization under the influence of actinic radiation, inparticular UV light, is the simplest way of polymerizing the monomers.This has the advantage that persons skilled in the art can choose thetemperature at which the mixture should be polymerized themselves. Thechoice of the temperature is often very important as theliquid-crystalline properties of the mixture to be polymerized aregoverned to a substantial degree by the temperature.

[0019] Preferably, the mixture to be polymerized also comprises monomershaving two or more reactive groups of the above-mentioned type. Duringpolymerization, the presence of such monomers leads to the formation ofa three-dimensional network. This causes the optical properties of theinventive retardation foil to become less sensitive to variations intemperature. In particular for foils which are employed at differenttemperatures, such a small temperature-dependence of the opticalproperties is very favorable.

[0020] Liquid-crystalline molecules which can be used within the scopeof the invention correspond to the general formula

A-B-M-(B)-(A)

[0021] In this formula, M represents a liquid-crystalline group.Suitable M groups are disclosed, inter alia, in U.S. Pat. No. 4,398,803and WO 95/24454. B represents a so-called spacer group. Dependent uponthe desired properties, the monomers used comprise one or two spacergroups. Spacer groups are also known from the above-mentioned Patentpublications. A represents a reactive group of the above-mentioned type.The liquid-crystalline molecules may comprise one or two reactivegroups. As stated above, a part of the liquid-crystalline molecules inthe mixture may be non-reactive. In that case, these molecules do notcomprise A-type groups.

[0022] A preferred embodiment of the display device is characterized inthat the polymerized material comprises liquid-crystalline moleculeswhich are provided, at one end, with a non-polar group and, at the otherend, with a polar group. The presence of this type of liquid-crystallinemolecules causes the liquid-crystalline material of the mixture to bepolymerized to assume the homeotropic phase at a short distance from thesubstrate. As a result, the desired ordering of the tilt in theliquid-crystalline material of the retardation foil takes place almostspontaneously. Consequently, in this case treatments with electricfields to induce said tilt are redundant. This simplifies themanufacture of such foils.

[0023] Liquid-crystalline molecules having a polar end and a non-polarend correspond to the general formula

R-B-M-Z

[0024] where B and M have the above-mentioned meaning. In this case, thespacer group B serves as the non-polar group of the molecule and Zrepresents a polar group, such as

[0025] —CN, —OH, —NO₂, —COOH or —C(O)O—CH₃. R represents a furthersubstituent.

[0026] A further preferred embodiment of the display device ischaracterized in that at the end provided with the non-polar group, theliquid-crystalline molecules are covalently bonded to the polymerized orvitrified material. This is achieved if for R use is made of a reactivegroup of the above-mentioned type. By virtue of this measure, theoptical properties of the inventive retardation foil become lesssensitive to variations in temperature. In particular for foils whichare employed at different temperatures, such a smalltemperature-dependence of the optical properties is very favorable.

[0027] The tilt may be substantially uniform. Alternatively, during themanufacture of the display device, a pretilt can be induced in one orboth boundary surfaces, for example by means of the method described inU.S. Pat. No. 5,155,610. Dependent upon this pretilt, the opticallyanisotropic layer may exhibit, for example, a “splay deformation”. Theeventual director profile can also be influenced, during themanufacture, by means of electric and/or magnetic fields. This mayresult, for example, in a preferred direction for the directors. Such apreferred direction can alternatively be attained during polymerizationin the smectic C-phase of liquid-crystalline materials.

[0028] These and other aspects of the invention will be apparent fromand elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the drawings:

[0030]FIG. 1 is a schematic, cross-sectional view of a part of aliquid-crystal display device in accordance with the invention,

[0031]FIG. 2 shows a part of the device shown in FIG. 1,

[0032]FIGS. 3a-3 d schematically explain the optical behavior of a knowndevice, which is similar to the one shown in FIG. 2, by means ofso-called indicatrices,

[0033]FIG. 4 schematically shows the differences between the displaydevice in accordance with the invention and the display device inaccordance with FIGS. 3a-3 d,

[0034]FIGS. 5 and 6 schematically show compensator layers in accordancewith the invention,

[0035]FIG. 7 shows iso-contrast curves of a display device in accordancewith the invention, and

[0036]FIGS. 8a-8 g show the structural formulas of a number of materialsused.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0037]FIG. 1 is a schematic, cross-sectional view of a part of aliquid-crystal display device comprising a liquid-crystal cell 1 with atwisted nematic, liquid-crystal material 2 sandwiched between twosubstrates 3, 4, for example, of glass, which are provided withelectrodes 5, 6. The device further comprises two polarizers 7, 8 whosedirections of polarization intersect each other at right angles. Thecell further includes orientation layers (not shown), which orient theliquid-crystal material on the inner surfaces of the substrates, in thisexample, in the direction of the polarization axes of the polarizers, sothat the cell has a twist angle of 90 degrees. In this case, theliquid-crystal material has a positive optical anisotropy and a positivedielectric anisotropy. If a voltage is applied to the electrodes 5, 6,the molecules and hence the directors are oriented in accordance withthe field. Thus, in an ideal case, all molecules extend substantiallyperpendicularly to both substrates (situation 11 in FIG. 2). Inpractice, however, this situation requires too high a voltage; atcustomary voltages, the molecules make a small angle with the normal tothe substrates 3, 4, which corresponds to situation 12 shown in FIG. 2.Consequently, when the cell is viewed from direction 13, the viewerlooks much more in the direction of the molecules, so that light whichis still passed at this voltage, is subject to a substantial and, inaddition, asymmetric angle-dependence. This angle-dependence can beexplained by means of the so-called “optical indicatrix”, i.e. athree-dimensional geometric display of the refractive index for eachdirection in which the vector of the electric-field component of thelight can oscillate. In the case of an optically isotropic material,this optical indicatrix is spherical, in the case of a bi-axial materialit is an ellipsoid and, in the case of uniaxial material it is anellipsoid with axial symmetry. As, in an ideal case, the liquid-crystalmaterial in the driven state is uniaxial across almost its entirethickness (in almost all molecular layers, except for a few molecularlayers near the substrates, the molecules extend at right angles to thesubstrates), situation 11 shown in FIG. 2 can be represented byindicatrix 14 in FIG. 3a, which is an ellipsoid whose main axis extendstransversely to the liquid-crystal layer, the refractive index n_(z) atright angles to the substrates being larger than the refractive index inthe planes extending parallel to the substrates (n_(x)=n_(y)).

[0038] As the liquid is not isotropic, birefringence occurs. It can bedemonstrated that this birefringence can be compensated for by anindicatrix 15 in FIG. 3b, which is an ellipsoid whose axis extendstransversely to the liquid-crystal layer, the refractive index n_(z) atright angles to the substrates being smaller than the refractive indexin the planes parallel to the substrates (n_(x)=n_(y)).

[0039] In practice, however, this situation requires too high a voltage;at the customary voltages, the molecules make a small angle with thenormal to the substrates 3, 4, which corresponds to situation 12 in FIG.2. As a result, when the cell is viewed from direction 13, a viewerlooks much more in the direction of the molecules. In this morepractical situation, the indicatrix 14′ has a main axis which makes asmall angle with the axis transverse to the liquid-crystal layer;indicatrix 14 is slightly tilted, as it were, relative to this axis. Inthis case, a good compensation is attained by a compensator layer 9having an indicatrix 15′, which is obtained by tilting, as it were,indicatrix 15 in the same manner relative to this axis.

[0040]FIG. 4 shows, on the left-hand side, the same situation, i.e. theliquid 2 with the associated indicatrix 14′, and the compensator layer 9with the associated indicatrix 15′; in this case, the liquid and thecompensator layer are sandwiched between crossed polarizers 7, 8. Asshown on the right-hand side of FIG. 4, the display device in accordancewith the invention comprises, in this example, two retardation foilswhich predominantly contain polymerized liquid-crystalline materialhaving a tilt angle of the liquid-crystal molecules in the polymerizedliquid-crystalline material with respect to the substrates and anaverage direction of orientation of the liquid-crystal molecules in thepolymerized liquid-crystalline material, which directions of orientation(in this example) make an angle of 90 degrees with each other, viewed atright angles to the substrates. In this example, the polymerizedliquid-crystal molecules of the retardation foil 9 ^(a) extend parallelto the direction of polarization of polarizer 8 and exhibit an averagetilt angle of 40 degrees. In this example, the polymerizedliquid-crystal molecules of retardation foil 9 ^(b) extend parallel tothe direction of polarization of polarizer 9 and also exhibit an averagetilt angle of 40 degrees. For a possible explanation of the operatingprinciple, the liquid layer 2 is divided into three parts which eachhave their own indicatrix 16, 17 and 18. Indicatrix 21 of retardationfoil 9 ^(a) now compensates, as it were, indicatrix 18 and a part ofindicatrix 17, while indicatrix 22 of retardation foil 9 ^(b) nowcompensates, as it were, indicatrix 16 and the other part of indicatrix17.

[0041] The average tilt angle in the retardation foils 9 ^(a), 9 ^(b)may also be different, for example 40 and 50 degrees, respectively,which is achieved, in this example, by causing, for example, the othersurface of retardation foil 9 ^(b) to engage the upper surface ofretardation foil 9 ^(a).

[0042] On the one hand, the average tilt angle in the retardation foils9 ^(a), 9 ^(b) is preferably larger than 10 degrees because smallerangles cause the difference in optical behavior between directionsparallel and anti-parallel to the projection of the directors on thesubstrate to be too small; on the other hand, this tilt angle shouldpreferably not exceed 70 degrees because, otherwise, the retardationfoils acquire too much axial symmetry as a function of the viewingangle. In the present case, the retardation layer is drawn in one piece,however, the layers may also be situated on either side of the liquid,or the entire layer may be situated on the other side of the liquid.

[0043] The associated iso-contrast curve is shown in FIG. 7. In thisFigure, Φ represents the azimuth angle and θ represents the polar anglebetween the direction of view and the normal to the substrate.

[0044] The retardation foils can be manufactured, for example, byproviding two glass plates (whether or not covered with ITO) withorienting layers, (for example polyimide rubbed in anti-paralleldirections so that a high tilt is attained) which glass plates are heldat a distance from each other by means of spacers. Between the glassplates, there is provided a suitable mixture of LC monomers, for examplea mixture of 25 wt. % C6M (FIG. 8a) and 74 wt. % 495 (FIG. 8b) and asuitable initiator, whereafter this mixture is polymerized by UVradiation at 100° C. under the influence of a weak electric field.

[0045] Another suitable mixture comprises 40 wt. % of a reaction LCmaterial (a mixture of 25 wt. % 296 (see FIG. 8c) and 75 wt. % 716 (seeFIG. 8e)) and 60% of a non-reactive cyanobiphenyl mixture. This mixturewas spin-coated onto a glass plate covered with rubbed polyimide andsubsequently polymerized by means of UV radiation in a nitrogenatmosphere. As, on the one hand, the molecules are oriented with a smalltilt angle on the polyimide, and, on the other hand, tend to alignhomeotropically on the surface, an average tilt angle α is obtained(FIG. 5). A similar structure is attained with molecules which assume ahomeotropic alignment on the substrate and a planar alignment on thesurface. This can alternatively be achieved by means of other methods(provision by means of a doctor blade) and substrates (directly ontoglass, onto a suitable synthetic resin such as cellulose triacetate).Another mixture, which did not comprise non-reactive liquid-crystallinematerial so that the strength of the layer was increased, was composedof 25 wt. % 296 (see FIG. 8c) and 75 wt. % 76 (see FIG. 8e).

[0046] A compensator layer 9 is obtained by joining two such retardationfoils having different tilt angles, the directions of orientation of themolecules being rotated through approximately 90 degrees with respect toeach other. FIG. 5 shows such a compensator layer comprising retardationfoils having different tilt angles. A substrate may be sandwichedbetween the foils. In this case, the director 23 of the polymerizedliquid-crystal molecules in retardation layer 9 ^(a) extends in theplane of the drawing, whereas the director 23 of the polymerizedliquid-crystal molecules in retardation layer 9 ^(b) extends in a planeat right angles to the plane of the drawing (FIG. 5).

[0047] In the case of retardation foils having a substantially constanttilt angle, use can also be made of reactive liquid-crystal molecules asthe starting material, which molecules are brought to the smecticC-phase between surfaces which bring about a homeotropic alignment,whereafter the molecules are polymerized again by means of UV radiation.In this manner, large tilt angles can be achieved (in the range between40 and 89 degrees). As the eventual setting is temperature-dependent,the eventual angle can be influenced via the temperature setting. By wayof example, use is made of a mixture comprising 54.5 wt. % C6H (No. 23)(see FIG. 8f), 44.5 wt. % No. 79 (see FIG. 8g) and a suitable initiator.The mixture was sandwiched between two glass plates which were providedwith a layer of a homeotropically aligning material, for example apolyimide such as SE 7511L which can be obtained from Nissan Chemical.The mixture was subsequently cooled from 155° Celsius (isotropic state)to 82° Celsius (smectic state). To attain a uniform alignment, a minorshift of the smectic layers may be advantageous. Subsequently, thereactive molecules were polymerized again by means of UV radiation. FIG.6 shows how two such retardation foils having a constant tilt angle βare combined into a compensator layer 9. Of course, the invention is notlimited to the above-mentioned examples. For example, the twist anglesof the display cell can be chosen to be unequal to 90 degrees, forexample in the range between 60 and 120 degrees; in general, the anglesbetween the directions of orientation of the retardation foils will alsobe adapted. Twist angles below 60 degrees lead to discoloration andimperfect extinction; twist angles above 120 degrees cause thetransmission/voltage curve to become so steep that grey levels can nolonger be realized.

[0048] It is not necessary that the directions of orientation of themolecules in the retardation foils extend parallel to the planes ofpolarization of the polarizers.

[0049] It is not necessary either to combine the retardation foils intoa single compensator; in an alternative embodiment one retardation foilis provided on the side of one polarizer and the other retardation foilis provided on the side of the other polarizer. In a further example theretardation foils are provided on the outer surface or the inner surfaceof the cell. In the latter case, they can be applied directly onto thesubstrates or on other layers present in the cell, for example on acolor filter or on a protective coating or top coating. If the hardnessof the retardation foil is sufficient, its small thickness (up toapproximately 0.5 Φm) renders it very suitable for use as a top coating.Besides, more than two retardation foils can be used. As mentionedhereinabove, according to the invention the foils are also obtained byvitrification of liquid-crystal molecules instead of polymerization.

[0050] In another embodiment viz. a colour liquid crystal display devicehaving a colour filter the retardation foil has a patterned structure ofdifferent retardation values (e.g. by varying its thickness) inregistration with elements of the colour filter.

[0051] For each separate colour the retardation of the associated partof the foil is optimized for a wavelength associated with said colour.

[0052] Instead of driving by means of electrodes on both supportingplates, as described hereinabove, alternative use is made of thermaladdressing or addressing via plasma (plasma-addressed LCD). In the caseof very large tilt angles in the retardation foils, it may even beadvantageous in specific cases to provide the molecular structure with atwist so that the direction of the maximum contrast can be varied.

[0053] In summary, the invention relates to a liquid-crystal displaydevice comprising a display cell and a plurality of retardation foils ofpolymerized or vitrified liquid-crystal material, which retardationfoils have substantially complementary indicatrices so that each one ofthe retardation foils brings about the compensation of approximatelyhalf the display cell in the driven state.

What is claimed is:
 1. A method of manufacturing a retardation foil,characterized in that a liquid-crystalline mixture in the smecticC-phase between two homeotropically aligning substrates is cured bymeans of polymerization.
 2. A method of manufacturing a liquid-crystaldisplay device having a display cell comprising: forming a layer of anematic, liquid-crystal material so as to have a twist angle which liesin a range of 60-120 degrees, between two substantially parallelsubstrates; forming first and second polarizers so as to have first andsecond polarizing directions and arranging the first and secondpolarizers on at least one of the substrates; and forming first andsecond retardation foils in a predetermined relationship with the firstand second polarizers, and so that the first and second retardationfoils respectively comprise polymerized or vitrified liquid-crystallinematerial comprising liquid-crystal molecules which are respectivelyarranged to: a) have average orientations which respectively extend infirst and second directions which directions are respectively parallelto first and second planes that are normal to the substrates, the firstand second planes being oriented with respect to one another at an anglein a range of 60 to 120 degrees; and b) exhibit first and second averagetilt angles relative to the substrates.
 3. A method as set forth inclaim 2, comprising: forming the first and second retardation foils sothat a twist angle of the liquid crystal material lies in one of theranges of 60-<90 and >90-120 and so that the angle with which the firstand second planes are oriented with respect to one another isessentially the same as the twist angle of the liquid crystal material.4. A method as set forth in claim 2, comprising: forming the retardationfoils so that an average tilt angle of the first retardation foil is 40degrees.
 5. A method as set forth in claim 2, comprising: forming theretardations foils so that an average tilt angle of the secondretardation foil is 40 degrees.
 6. A method as set forth in claim 2,comprising: forming the first and second polarizers so that the firstand second polarizing directions are oriented at right angles to eachother.
 7. A method as set forth in claim 2, comprising: forming thefirst and second polarizers so that the first and second polarizingdirections are non-parallel with the first and second planes.
 8. Amethod as set forth in claim 2, comprising: orienting the liquid-crystalmolecules in the polymerized or vitrified liquid-crystalline material soas to be substantially constant in at least one of the retardationfoils.
 9. A method as set forth in claim 2, comprising: varying the tiltangle of the liquid-crystal molecules in the polymerized or vitrifiedliquid-crystalline material, in at least one of the retardation foils,in a direction at right angles to the foil.
 10. A method as set forth inclaim 9, comprising: forming the retardation foils so that the averagetilt angle of the liquid-crystal molecules in the polymerized orvitrified liquid-crystalline material is at least 10 degrees.
 11. Amethod as set forth in claim 2, comprising: forming the retardationfoils so that the tilt angle of the liquid-crystal molecules in thepolymerized or vitrified liquid-crystalline material is substantiallyconstant in at least one of the retardation foils.
 12. A method as setforth in claim 2, comprising: forming the retardation foils so that thetilt angle of the liquid-crystal molecules in the polymerized orvitrified liquid-crystalline material is at least 10 degrees and at most70 degrees.
 13. A method as set forth in claim 2, comprising: formingthe retardation foils so that the polymerized or vitrified materialcomprises liquid-crystalline molecules which have, at one end, anon-polar group and, at the other end, a polar group.
 14. A method asset forth in claim 13, wherein, at the end having the non-polar group,the liquid-crystalline molecules are covalently bonded to thepolymerized or vitrified material.
 15. A method as set forth in claim 2,comprising: forming the retardation foils so that the direction oforientation of the liquid-crystal molecules in the polymerized orvitrified liquid-crystalline material is substantially constant in atleast one of the retardation foils.
 16. A method as set forth in claim2, comprising: forming the retardation foils so that the tilt angle ofthe liquid-crystal molecules in the polymerized or vitrifiedliquid-crystalline material varies in at least one of the retardationfoils.
 17. A method as set forth in claim 2, comprising: forming theliquid-crystal molecules in the polymerized or vitrifiedliquid-crystalline material so that the tilt angle is substantiallyconstant in at least one of the retardation foils.
 18. A method as setforth in claim 2, comprising: forming the polymerized or vitrifiedmaterial so that the liquid-crystalline molecules are provided, at oneend, with a non-polar group and, at the other end, with a polar group.19. A method as set forth in claim 2, comprising: forming theliquid-crystalline molecules at the end provided with the non-polargroup so that the liquid-crystalline molecules are covalently bonded tothe polymerized or vitrified material.
 20. A method of manufacturing acompensator layer comprising: forming first and second retardation foilsby polymerizing or vitrifying liquid-crystalline material comprisingliquid-crystal molecules in manner wherein the liquid-crystal moleculesin the polymerized or vitrified liquid-crystalline material of the firstand second retardation foils respectively exhibit first and second tiltangles which are respectively parallel to first and second planes thatare normal to major surfaces of the foils and that are angled withrespect to one another by an angle of 60-120 degrees.
 21. A method asset forth in claim 20, wherein the forming of the first and secondretardation foils is such that the angle between the first and secondplanes are that normal to the major surfaces of the foils lies in one ofthe ranges of 60-<90 and >90-120 degrees.
 22. A method as set forth inclaim 20, wherein the liquid-crystalline material comprises a reactionproduct of a monomers or of a mixture of monomers having a reactivegroup and which can be oriented prior to polymerization.
 23. A method asset forth in claim 22, wherein the reactive group comprises one of avinyl ether, a thiolene system, an epoxy group and a (meth)acrylategroup.
 24. A method as set forth in claim 22, wherein the monomers arepolymerized using thermal polymerization or under the influence ofactinic radiation.
 25. A method as set forth in claim 24, wherein theactinic radiation comprises UV light.
 26. A method as set forth in claim24, further comprising the step of selecting the temperature at whichthe mixture is polymerized.
 27. A method as set forth in claim 22,wherein the mixture comprises monomers having two or more reactivegroups which during polymerization lead to the formation of athree-dimensional network.
 28. A method as set forth in claim 20,comprising: preparing liquid-crystal molecules which are provided, atone end, with a non-polar group and, at the other end, with a polargroup; applying the liquid-crystalline molecules to a substrate so thatthey assume a homeotropic phase proximate the substrate and so that adesired ordering of the tilt in the liquid-crystalline material of theretardation foil takes place almost spontaneously and obviates treatmentwith an electric field to induce the tilt.
 29. A method of forming aliquid-crystal display device having a display cell comprising: formingretardation foils on substrates using polymerized or vitrifiedliquid-crystal material wherein the liquid-crystal molecules of thepolymerized or vitrified liquid-crystal material have a tilt angle withrespect to a plane parallel to the substrates and so that theretardation foils have substantially complementary indicatrices and sothat each one of the retardation foils brings about the compensation ofapproximately half the display cell in the driven state.